I have a Black & Decker EPC128 12V cordless drill. It has two batteries. Since the recharger has no light or indicator on it, I never surely understand whether the battery is partly/fully charged or overcharged. How long exactly should I recharge the batteries? The tool is something like this:

Yeah, I would have issues with no blinky light, especially as some batteries (NiMH) can be overcharged which will shorten their lifespan. My Ryobi ONE+ NiMH charger has TWO blinky lights (!) and it's a smart charger that'll go into trickle-charge mode to protect a battery that's left in it overnight (or longer).
–
KeithSMar 5 '12 at 16:06

4

Pretty sad as overcharging kills NiCad and NiMH batteries. There are many specialized chips that understand the charge cycle of both these battery chemistries and can sense when the maximum charge is reached and the cycle is complete for termination. Even cheap Chinese knockoff stuff includes smart charging. It's one of the reasons I've moved away from Black & Decker tools, they've gone too damn cheap. Overcharging also lights LiPoly batteries on fire, so if you don't have a smart balance charge system with that battery chemistry, you'll eventually pay for the cheapness.
–
Fiasco LabsJan 19 '13 at 19:32

2 Answers
2

After approx. 3 hours of charging, the battery will be sufficiently
charged for use in regular applications. After approx. 8-10 hours of
charging, the battery will be fully charged.

After a few lines, it says:

After normal use, a charging time of 3 hours will provide sufficient
power for most applications. However, further charging for up to 6 hours
could significantly increase the use time, depending on the
battery and charging conditions.

Plug the charger (6) into any standard 120 Volt 60 Hz electrical outlet and let the battery pack charge initially for 12 hours. After the initial charge, under normal usage, your power pack should be fully charged in 6 to 12 hours.